Composition and Process for Enhanced Properties of Ferrous Components

ABSTRACT

Components, such as gears and other power transmission components, are formed by near-net-forging a high strength, high toughness ferrous metal alloy, surface processing metal alloy to form a hardened surface region ( 28 ), and coating the surface region with a lubricious coating ( 84 ) as shown in FIG.  9.

BACKGROUND OF THE INVENTION

The present invention relates generally to the combination ofnear-net-shape (NNS) forging, a class of high-strength, high-toughness(HSHT) ferrous alloys, and the application of thermo-chemical processingto enhance the surface properties of the alloy class forgings. Moreparticularly, the invention relates to applying the NNS forging, alloyselection, and thermo-chemical processing to gears and other componentswithin power transmission systems.

Conventional methods for producing, for example, gears involve manysequential processing steps. Typically, a forged billet stock is hobbedto a rough, oversized finish shape and thermo-chemically processed by,for example, carburization, then slow cooled. This is followed by stepsof re-austenitization, quenching, refrigerating by cryogenic treatment,tempering (aging), finish grinding, etch inspection, shot-peening,honing, and final inspection. These methods lead to extendedmanufacturing process time and increased costs.

Conventional hobbing of ferrous alloy blanks produces gear teeth shapesby cutting through any peripheral structural texture, or preferred grainorientation, that may be present in the blank from any prior formingoperations, thereby reducing performance benefits that can accrue fromthe forming operations.

Alloys used for gear applications need, for example, the ability towithstand shear strain, bending fatigue loads, and surface degradationvia pitting and contact wear. Conventional gear alloys are still limitedin the strength and toughness required for very high performanceapplications.

Surface engineering processes, including thermo-chemical treatments, aretypically required to improve the performance of conventional alloys.For iron-based metal alloy components, such as power-transmissioncomponents, it is often desirable to form a hardened surface case aroundthe core of the component to enhance component performance. The hardenedor chemically altered surface case provides wear and corrosionresistance, while the core provides toughness, impact resistance, andbending-fatigue strength.

There are various conventional methods for forming a hardened surfacecase on a power-transmission component fabricated from a steel alloy,while retaining the original hardness, strength, and toughnesscharacteristics of the alloy. Conventional methods used to achieve theproperties include carburizing and nitriding; alternatively, novel,unconventional thermo-chemical processes, such as high current densityion implantation, may be applied to achieve or retain desired case andcore properties.

The methods for forming a hardened surface case on gears, for example,also involve many sequential processing steps that increasemanufacturing time and cost.

Thus, there remains a need for reducing the time and costs formanufacturing gears, improving the properties and performance attributescompared to cut gears, and identifying a class of alloys having improvedstrength and toughness that are suitable for the application of thethermo-chemical treatments.

SUMMARY OF THE INVENTION

The disadvantages and limitations of the background art discussed aboveare overcome by the present invention. With this invention, thenear-net-shape forging process, producing a gear, for example,eliminates the need for hobbing the gear and augments the mechanicalproperties, which are further improved by the use of a class of HSHTferrous alloys possessing improved high-strength and high-toughness. Thealloy class has surface properties that may be enhanced throughthermo-chemical surface processing via methods that also reducemanufacturing time and costs, and the surface roughness of as-processedarticles may be isotropically superfinished via chemo-mechanical meansto further enhance the surface properties, including pitting fatigue andwear resistance.

An embodiment of the invention is a method whereby a billet of alloy isnear-net-shaped forged to the finished gear shape, but with a smallstock allowance for any subsequent heat treatment and thermo-chemicalsurface processing prior to finish machining and superfinishing.

Another embodiment of the invention is a method wherein the gear alloyis a selected from a class of high-strength, high-toughness alloys.

Another embodiment of the invention is a method wherein thenear-net-shape forged high-strength, high-toughness alloys are heattreated and thermo-chemically processed, such as to synergisticallycombine selected surface engineering and bulk alloy heat treatmentsteps, thereby effecting significant savings in processing times, cost,and delivery, while retaining the desired increase in performancecapability.

Another embodiment of the invention is a method wherein thenear-net-shape forging comprising the high-strength, high-toughnessalloys that are heat treated and thermo-chemically processed tosynergistically combine selected surface engineering and bulk alloy heattreatment steps, are further afforded a subsequent chemo-mechanicalprocessing step to reduce the surface roughness and further enhance theresulting surface properties, while retaining the desired increase inbulk and surface performance capabilities.

It may therefore be seen that the present invention teaches thecombination of near-net-shape (NNS) forging, a class of high-strength,high-toughness (HSHT) ferrous alloys and the application ofthermo-chemical processing to enhance the surface properties of thealloy class forgings.

The combination comprises a novel approach to the improvement ofcomponent or system properties, for example, to enhance the bending- andsurface-fatigue design allowables for gears and other components withinpower-transmission systems.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a metal alloy.

FIG. 2 shows a schematic view of a crystal structure.

FIG. 3 shows a schematic view of a metal alloy during surfaceprocessing.

FIG. 4 shows a schematic view of a metal alloy and hardened surfaceregion.

FIG. 5 shows a schematic view of a plasma (ion) nitriding chamber.

FIG. 6 shows a nitrogen concentration profile over a depth of a hardenedsurface region.

FIG. 7 shows a schematic view of a nitride compound on a surface regionof a metal alloy.

FIG. 8 shows a schematic view of a coating on a hardened surface regionof a metal alloy.

FIG. 9 shows a schematic view of a coating on an intermediate coating ona surface region of a metal alloy.

DETAILED DESCRIPTION

FIG. 1 shows a schematic view of a metal alloy 10, including a core 12and a surface region 14 on the core 12. The metal alloy 10 is aniron-based alloy that is generally nitrogen-free and has an associatedcomposition and hardening heat treatment, including a tempering or agingtemperature. The tempering or aging temperature is dependent on themetal alloy 10 composition and is the temperature at which the metalalloy is heat processed to alter characteristics of the metal alloy 10,such as hardness, strength, and toughness.

The composition of the metal alloy 10 is essentially a Ni—Co secondaryhardening martensitic steel, which provides high strength and hightoughness. That is, the ultimate tensile strength of the metal alloy 10is greater than about 170 ksi and the yield stress is greater than about140 ksi and in some examples the ultimate tensile strength isapproximately 285 ksi and the yield stress is about 250 ksi. Highstrength and high toughness provide desirable performance in suchapplications as power transmission components. Conventional vacuummelting and remelting practices are used and may include the use ofgettering elements including, for example, rare earth metals, Mg, Ca,Si, Mn and combinations thereof, to remove impurity elements from themetal alloy 10 and achieve high strength and high toughness. Impurityelements such as S, P, O, and N present in trace amounts may detractfrom the strength and toughness.

Preferably, the alloy content of the metal alloy 10 and the tempering(aging) temperature satisfy the thermodynamic condition that the alloycarbide, M₂C where M is a metallic carbide-forming element, is morestable than Fe₃C (a relatively coarse precursor carbide), such that Fe₃Cwill dissolve and M₂C alloy carbides precipitate. The M₂C alloycarbide-forming elements contribute to the high strength and hightoughness of the metal alloy 10 by forming a fine dispersion of M₂Cprecipitates that produce secondary hardening during a conventionalprecipitation-heat process prior to any surface processing. Thepreferred alloy carbide-forming elements include Mo and Cr, whichcombine with carbon in the metal alloy 10 to form M₂C. Preferably, themetal alloy 10 includes between 1.5 wt % and 15 wt % Ni, between 5 wt %and 30 wt % Co, and up to 5 wt % of a carbide-forming element, such asMo, Cr, W, V or combinations thereof, which can react with up toapproximately 0.5 wt % C to form metal carbide precipitates of the formM₂C. It is to be understood that the metal alloy 10 may include any oneor more of the preferred alloy carbide-forming elements.

The carbide-forming elements provide strength and toughness advantagesbecause they form a fine dispersion of M₂C. Certain other possiblealloying elements such as Al, V, W, Si, Cr, may also form othercompounds such as nitride compounds. These alloying elements and thecarbide-forming elements influence the strength, toughness, and surfacehardenability of the metal alloy 10.

Typically, metal alloy 10 is hardened by heat treating above ˜1500° F.in the austenite phase region (austenitizing) to re-solution carbides,etc. It is then quenched and refrigerated at approximately − (minus)100° F. to transform the austenite structure to martensite. The latteris a very hard, brittle, metastable phase having a body-centeredtetragonal (BCT) crystal structure because of the entrapped carbonatoms. Hence, at this stage, the core 12 and surface region 14 of themetal alloy 10 have a generally equivalent tetragonal crystal structure16 (FIG. 2).

As illustrated in FIG. 2, the tetragonal crystal structure 16 includesatomic lattice sites 17 forming sides having length 18 which areessentially perpendicular to sides having length 20. In the tetragonalcrystal structure 16, the length 18 does not equal the length 20.Subsequent aging heat treatments are used to both soften the martensitestructure and also transform the Fe₃C phase to M₂C which strengthens thestructure. The latter reaction tends to dominate, leading to secondaryhardening. These reactions can lead to concomitant changes in crystalstructure as the metastable martensitic BCT structure transitions toother phases, such as austenite and/or ferrite depending on the exposuretemperature and time. It is to be understood that the iron-based alloymay be formed instead with other crystal structures such as, but notlimited to, face-centered cubic (e.g. austenite) and body-centered cubic(e.g. ferrite). These phase transitions may lead to dimensional changes.

FIG. 3 shows a schematic cross-sectional view of the metal alloy 10during transformation of the surface region 14 into a hardened surfaceregion 28 as illustrated in FIG. 4. A high current density ionimplantation (high intensity plasma ion processing) nitriding process isused to form the hardened surface region, although other surfacehardening processes may be utilized such as, but not limited to,nitrocarburizing, carburizing, boronizing, and chromizing.

The high current density ion implantation (high intensity plasma ionprocessing) nitriding process is conducted in an appropriate reactor, anexample of which is illustrated schematically in FIG. 5. The metal alloy10 is placed in the reactor 34. The metal alloy 10 is placed in the highcurrent density ion implantation (high intensity plasma ion processing)chamber 36 on a cathode 38. The cathode 38 provides a voltage bias tothe metal alloy 10, thereby heating the metal alloy 10 to a desiredtemperature that is below the heat treating temperature, such as anaging or tempering temperature, of the metal alloy 10.

Heating the metal alloy 10 to a temperature above the heat treatingtemperature may alter the incumbent crystal structure 16, relieveresidual stresses in the metal alloy 10, otherwise undesirably alter themicrostructure and properties of the core, and undesirably alter thedimensions of the metal alloy 10. By utilizing a temperature that istypically below the heat treating temperature of the metal alloy 10, thestrength, toughness, incumbent crystal structure 16, and dimensions ofthe metal alloy 10 are maintained through the high current density ionimplantation (high intensity plasma ion processing) nitriding process.Subsequent processes to dimensionalize the metal alloy 10 or a powertransmission component formed from the metal alloy 10 are eliminated.For the preferred metal alloy 10 composition the heat treatingtemperature is between 700° F. and about 1000° F. For othercompositions, the heat treating temperature may be different.

The chamber 36 includes a vacuum pump 40 which maintains a vacuum in thechamber 36 of the reactor 34. A sample bias device 42 provides a biasvoltage of between 100V and 1500V to the cathode 38. Preferably, thebias voltage is between 150V and 700V. A thermocouple 44 attached to thecathode 38 detects the cathode 38 temperature and a cooling system 46provides cooling capability to control the chamber 36 temperature. Thechamber 36 is in fluid communication with precursor gases in storagetanks 48. The precursor gas storage tanks 48 may include gases such asnitrogen, hydrogen, and methane, although it should be noted that thesegases are not all necessarily utilized during the high current densityion implantation (high intensity plasma ion processing) nitridingprocess. The conduit 50 connects the precursor gas storage tanks 48 tothe inner chamber 40 and includes a gas metering device 52 to controlthe gas flow from the gas storage tanks 48. A plasma discharge voltagedevice at the filament 54 provides an ionizing voltage to a filament 56,which ionizes incoming gas from the conduit 50. The plasma dischargevoltage at the filament is preferably between 30V and 150V and even morepreferably is about 100V. It is to be understood that the configurationof the reactor 34 is not meant to be limiting and that alternativeconfigurations of high current density ion implantation (high intensityplasma ion processing) reactors as well as reactors utilizingalternative surface processing processes may be used.

The temperature, vacuum pressure in the chamber 36, precursor gas flowand ratio, time of processing, filament bias voltage, and sample biasvoltage are controlled during the high current density ion implantation(high intensity plasma ion processing) nitriding process to provide ahardened surface region 28 (FIG. 4) on the metal alloy 10. The preferredconditions include a temperature between 700° F. and about 1000° F., apressure between about 0.5 mtorr and 5.0 mtorr in the chamber 36, aprecursor gases mixture of nitrogen and hydrogen in the range 10 to 100%nitrogen and a preferred range of 80 to 100% nitrogen, and a time in therange of about 5 to 200 hours and a preferred range of 10 to 100 hours.Even more preferably, the conditions are controlled to a temperature ofabout 800° F. to about 875° F., a pressure of 0.75 mtorr in the chamber36 (FIG. 5) and for a time of about twelve hours depending on the casedepth required.

Under the preferred conditions, nitrogen from the nitrogen atmosphere 26(FIG. 3) in the chamber 36 diffuses into the surface region 14 of themetal alloy 10. The nitrogen interstitially diffuses into the surfaceregion 14, thereby hardening the surface region 14 and transforming thesurface region 14 into the hardened surface region 28. During thisprocess, ions from the chamber 36 also bombard the surface region 14without diffusing into the surface region 14. That is, the ions sputterthe surface region 14 and thereby remove oxides and other impuritiesthat may be present on the surface region 14. Additionally, the biasvoltages utilized for the sample bias and filament voltage may providethe benefit of more favorable processing kinetics compared to othernitriding processes that utilize lower operating voltages, such asplasma (ion) nitriding.

Preferably, the hardened surface region 28 has a gradual transition innitrogen concentration over a depth D between an outer surface 30 of thehardened surface region 28 and an inner portion 32 of the hardenedsurface region 28.

The line 62 in FIG. 6 illustrates a gradual nitrogen concentrationprofile over the depth D. By comparison, the line 64 represents thenitrogen concentration profile of a generally abrupt nitrogenconcentration. For the line 62, at a shallow depth into the hardenedsurface region 28 such as near the outer surface 30, the nitrogenconcentration is relatively high compared to the nitrogen concentrationin the core 12. At a deeper depth, such as near the inner portion 32,the nitrogen concentration is relatively low and approaches the nitrogenconcentration of the core 12. It is to be understood that a variety ofnitrogen concentration profiles may result from varying the preferredconditions.

FIG. 7 shows a schematic view of a metal alloy 10 after another highcurrent density ion implantation (high intensity plasma ion processing)nitriding process. Utilizing a temperature towards the ends of thepreferred range of 700° F. and about 1000° F. or utilizing an additionalgas such as methane may result in the formation of a compound 68 of ironand nitrogen, such as the γ′ or ε compounds, on the surface region 14.Formation of the compound 68 is generally not preferred if a coatingwill be subsequently deposited over the compound 68, however, thecompound 68 may provide corrosion resistance for the metal alloy 10.

Additionally, alloying elements such as Al, V, W, Si, and Cr may bepresent in the metal alloy 10. Nitride compounds containing the alloyingelements may form during the high current density ion implantation (highintensity plasma ion processing) nitriding process. The presence of thenitride compounds is generally detrimental to the mechanical propertiesof the metal alloy 10 and are particularly detrimental in a complex withiron nitride compounds that may be formed under certain nitridingprocessing conditions; however, the presence of these alloying elementsmay be required to acquire other characteristics in the metal alloy 10.

FIG. 9 shows a schematic view of a metal alloy 10 after a high currentdensity ion implantation (high intensity plasma ion processing)nitriding process. The metal alloy 10 includes a coating 84 on thehardened surface region 28, which preferably has a gradual nitrogenconcentration profile and essentially does not include an iron andnitrogen compound, such as the γ′ or ε compounds. The coating 84 isdeposited on the hardened surface region 28 in a thickness between 0.5micrometers and 10 micrometers by a vapor deposition or magnetronsputtering process, although other thicknesses may be desirable. Knownchemical vapor deposition, physical vapor deposition, andplasma-assisted chemical vapor deposition are preferred vapor depositionprocesses; however, it is to be understood that other or hybriddeposition processes may be utilized.

The deposited coating 84 is a solid lubricious coating such as anamorphous hydrogenated carbon, although other coatings may be used. Theamorphous hydrogenated carbon coating has a biaxial residual stress lessthan 800 MPa in compression at room temperature, is thermally stable attemperatures over 400° F., and has an abrasive wear rate less than3×10⁻¹⁵ m³m⁻¹N⁻¹ in a slurry of Al₂O₃. The amorphous hydrogenated carboncoating may include a metal or transition metal such as titanium,chromium, tungsten or other transition metal to alter the lubriciouscharacteristics of the coating 84. It should be noted that the abovedescription represents a non-limiting example of the many types of asolid lubricious coating that may be applied to the surface of an alloyor component to improve certain performance characteristics.

Referring to FIG. 9, an intermediate coating 86 may be deposited betweenthe coating 84 and the hardened surface region 28 to strongly bond thecoating 84 to the hardened surface region 28. The intermediate coating86 bonds strongly to both the hardened surface region 28 and the coating84. Preferably, the intermediate coating 86 is a metal and even morepreferably it is the same transition metal as is included in theamorphous hydrogenated carbon coating. Generally, like materials, suchas two metals, form stronger bonds than unlike materials, such as ametal and a non-metal. Therefore, the metal of the intermediate coating86 strongly bonds to the metal hardened surface region 28 and to thetransition metal in the amorphous hydrogenated carbon coating.

Methods for producing gears, for example, involve many sequentialprocessing steps. Typically, a forged billet stock is hobbed to a rough,oversized finish shape and thermo-chemically processed by carburization,for example, then slow cooled. This is followed by the mandatory oroptional steps of re-austenitization, quenching, refrigerating bycryogenic treatment, tempering (aging), finish grinding, etchinspection, shot-peening, honing and final inspection. The methods leadto extended manufacturing process time and increased costs.

The near-net-shape forging process, producing a gear, for example,eliminates the need for hobbing the gear. The near-net-forging processbenefits mechanical properties by promoting the material flow to followthe contours of the gears. This texturing also leads to microstructuralalignment that promotes improvements in mechanical properties, includingtooth bending fatigue.

When the gear material is selected from the the class of high-strength,high toughness ferrous alloys, the performance of the gear is furtherimproved.

The alloy class has surface properties that may be enhanced throughthermo-chemical surface processing via methods that also reducemanufacturing time and costs.

In addition, the performance characteristics of gears, bearings, andother components within a power-transmission system may be improved bythe refinement in the roughness of the surfaces of such componentsthrough a process of superfinishing. One suitable superfinishingtechnique is described in U.S. Pat. No. 4,491,500, which discloses aprocess for refining metal surfaces in which a two-step processemploying a liquid chemical is followed by a burnishing liquid. Arelatively soft coating is formed, which is subsequently treated andphysically removed. In the technique, a mass of elements, comprised of aquantity of objects with hard metal surfaces of arithmetic averageroughness value in excess of about 15 microinches, is introduced intothe container of mass finishing equipment. The mass of elements iswetted with a liquid substance capable of rapid reaction, underoxidizing conditions, to chemically convert the metal of the objectsurfaces to a stable film of substantially reduced hardness, and themass is rapidly agitated, while maintaining the metal surfaces in awetted condition with the liquid substance, to produce relative movementand abrasive contact among the elements thereof and to producecontinuous oxygenation of the liquid substance. The reactivity of theliquid substance and the intensity of agitation of the mass arecontrolled to maintain the stable film on the metal surfaces at least atthe level of visual perceptibility. Agitation is continued for a periodsufficient to produce a finish of arithmetic average roughness less thanabout 14 microinches, and preferably less than about 10 microinches;thereafter, the objects will generally be treated to dissolve the stablefilm from the metal surfaces. In the preferred embodiments of thetechnique, the mass of elements introduced into the mass finishingequipment will include a quantity of abrasive finishing media, and theagitation step will be carried out for a period of less than six hours.Generally, the surfaces will be of a metal selected from the groupconsisting of iron, copper, zinc, aluminum, titanium, and the alloysthereof, and the stable film will comprise an oxide, phosphate, oxalate,sulfate, and/or chromate of the substrate metal. Thus, the liquidsubstance utilized to chemically convert the metal of the objectsurfaces will usually be a solution containing one or more of theradicals: phosphate, oxalate, sulfate, chromate, and mixtures thereof,and in certain instances it will be preferred for the substance toadditionally include an oxidizing agent; generally, the liquid substancewill have an acidic pH value. Solutions containing phosphate and oxalateradicals in combination with a peroxide compound are often found to beparticularly effective for refining ferrous metal surfaces, and may beproduced from a tripolyphosphate salt, oxalic acid, and hydrogenperoxide.

It may therefore be appreciated from the above detailed description ofthe preferred embodiment of the present invention that the combinationof selection of a member of the class of high-strength, high-toughness(HSHT) ferrous alloys and its processing to include near-net-shape (NNS)forging, thermo-chemical processing, a vibratory, chemo-mechanicalprocess (chemically accelerated vibratory polishing), such assuperfinishing, to enhance the surface properties of the alloy classforgings, and coating the surface;

comprises a novel approach to the improvement of component or systemproperties. For example, the combination enhances the bending- andsurface-fatigue design allowables for gears and other components withinpower-transmission systems.

Accordingly, the primary advantages of the present invention include:the identification of near-net-shape forging processes that eliminatehobbing while imparting enhanced strength, including axial- andbending-fatigue strength, the use of a new class of ferrous alloyspossessing improved high-strength and high-toughness compared toconventional gear alloys, thermo-chemically processing them viaconventional and/or novel means to enhance surface properties, reductionof the surface roughness of the as-thermo-chemically processed article,also to enhance surface properties and performance, and combining theseelements in such a manner that the surface and bulk properties andperformance are enhanced and manufacturing time and casts are reduced.

Although an exemplary embodiment of the present invention has been shownand described with reference to particular embodiments and applicationsthereof, it will be apparent to those having ordinary skill in the artthat a number of changes, modifications, or alterations to the inventionas described herein may be made, none of which depart from the spirit orscope of the present invention. All such changes, modifications, andalterations should therefore be seen as being within the scope of thepresent invention.

Although the foregoing description of the present invention has beenshown and described with reference to particular embodiments andapplications thereof, it has been presented for purposes of illustrationand description and is not intended to be exhaustive or to limit theinvention to the particular embodiments and applications disclosed. Itwill be apparent to those having ordinary skill in the art that a numberof changes, modifications, variations, or alterations to the inventionas described herein may be made, none of which depart from the spirit orscope of the present invention. The particular embodiments andapplications were chosen and described to provide the best illustrationof the principles of the invention and its practical application tothereby enable one of ordinary skill in the art to utilize the inventionin various embodiments and with various modifications as are suited tothe particular use contemplated. All such changes, modifications,variations, and alterations should therefore be seen as being within thescope of the present invention as determined by the appended claims wheninterpreted in accordance with the breadth to which they are fairly,legally, and equitably entitled.

1. A method of producing a component, the method comprising:near-net-shape forging a high strength, high toughness ferrous metalalloy to an essentially finished shape component; and surface processingthe component with high current density ion implantation to form ahardened surface region; and reducing surface roughness of the componentwith a vibratory, chemo-mechanical superfinishing process.
 2. The methodof claim 1, wherein the component is a power transmission component. 3.The method of claim 2, wherein the power transmission component is agear.
 4. The method of claim 1, wherein the surface processing comprisesat least one of nitriding, nitrocarburizing, carburizing, boronizing,and chromizing.
 5. (canceled)
 6. The method of claim 1, and furthercomprising: heat treating the component; quenching the component;refrigerating the component; and tempering the component.
 7. The methodof claim 1, and further comprising: forming a solid lubricious coatingover the surface region.
 8. The method of claim 7, wherein the solidlubricious coating comprises amorphous hydrogenated carbon.
 9. Themethod of claim 8, wherein the solid lubricious coating includes atransition metal.
 10. The method of claim 7, and further comprising:forming an intermediate coating over the surface region prior to formingthe solid lubricious coating.
 11. The method of claim 10, wherein theintermediate coating comprises a metal.
 12. The method of claim 11wherein the solid lubricious coating comprises amorphous hydrogenatedcarbon the metal contained in the intermediate coating.
 13. The methodof claim 1, wherein the ferrous metal alloy comprises at least 5 wt %cobalt, at least 1.5 wt % nickel, up to 1.0 wt % carbon, and up to 15 wt% of molybdenum, chromium, tungsten, or vanadium and combinationsthereof. (canceled)
 15. (canceled)
 16. A method of producing acomponent, the method comprising: near-net-forging a ferrous metal alloyto an essentially finished component shape; transforming a surfaceregion of the metal alloy to a hardened surface region with a highcurrent density ion implantation process; forming a coating over thehardened surface region; and reducing surface roughness with avibratory, chemo-mechanical superfinishing process, in which saidvibratory, chemo-mechanical process is provided before and/or after saidcoating.
 17. The method of claim 16, wherein the metal alloy has acomposition comprising at least 5 wt % cobalt and at least 1.5% nickel,18. The method of claim 16, wherein the metal alloy has a compositioncomprising up to 1.0 wt % carbon, and up to 15 wt % of molybdenum,chromium, tungsten, or vanadium and combinations thereof.
 19. The methodof claim 16, wherein the coating comprises an amorphous hydrogenatedcarbon coating.
 20. The method of claim 16, and further comprisingforming an intermediate coating between the coating and the hardenedsurface region.
 21. The method of claim 20, wherein the intermediatecoating comprises a transition metal.
 22. (canceled)
 23. (canceled)